Wireless systems such as the long term evolution-advanced (LTE-A) may use multiple spectrum segments, also termed “component carriers” to accommodate flexible bandwidth requirements. Each segment may have a fixed or configurable frequency spectrum width, such as 20 MHz. While one segment may be permanently allocated for an LTE-A base station known as evolution Node B (eNodeB), thus termed “primary component carrier”, others may be shared with nearby base stations, depending on resource availability, traffic volume, the number of user equipments (UEs) served by each eNodeB and the like.
Normal baseband signal generation of an orthogonal frequency-division multiplexing (OFDM) signal that occupies a single component carrier as used in a LTE-A downlink may need spectrum shaping filtering to rid of unwanted out-of-band emissions. This is because a discontinuity often occurs between the waveforms of an OFDM symbol and the cyclic prefix of the next adjacent OFDM symbol. The discontinuity causes undesired spectral leakage into nearby frequency bands that may need to be suppressed by filtering.
Filtering such as spectrum shaping filtering may be performed by at least one digital filter operating on a digital complex baseband signal that comprises a real part and an imaginary part. For a single component carrier transmission, the frequency response of the filtering operation may be symmetrical relative to the frequency of 0 Hz. A digital filter having a symmetric frequency response can be implemented using a real-valued filter operating on the real part of the signal, and another real-valued filter operating on the imaginary part of the signal.